Bilingualism Tied to Better Post-stroke Cognition

Pauline Anderson

November 20, 2015

Speaking a second language appears to give patients an advantage in terms of post-stroke cognitive health.

A new study of stroke survivors showed that more than twice as many bilingual patients as monolingual patients had intact cognitive function after a stroke event. Being able to speak more than one language was an independent predictor of post-stroke cognitive function.

The study "adds to the body of evidence" that bilingualism can result in a better cognitive outcome, "even in an acute brain event like stroke," said lead author Suvarna Alladi, DM, who at the time of the study was at Nizam's Institute of Medical Sciences in Hyderabad, India, and is now professor, neurology, National Institute of Mental Health and Neurosciences, Bangalore, India.

Dr Suvarna Alladi

Being bilingual is just one way to try to boost brain power; others include playing a musical instrument or doing Sudoku puzzles on a regular basis, Dr Alladi noted.

The study was published online November 19 in Stroke.

The analysis included 608 adult participants from the stroke registry at Nizam's Institute of Medical Sciences who had sustained an ischemic stroke and were evaluated within 3 to 24 months.

Those who were bilingual and those who spoke only one language were similar in terms of age (mean, 57.0 and 56.6 years, respectively). The two groups were also similar in terms of vascular risk factors; for example, 61.2% of bilingual and 64.3% of monolingual patients had hypertension and 35.7% of both groups had diabetes mellitus.

To evaluate cognition, researchers used the Addenbrooke's Cognitive Examination-Revised, a multidimensional cognitive screening tool adapted for Telugu- and Hindi-speaking populations. They used the Clinical Dementia Rating scale to assess severity of dementia. All patients underwent brain imaging.

Vascular dementia was diagnosed in 31.1% of patients, vascular mild cognitive impairment in 26.2%, aphasia in 11.0%, and normal cognition in 31.7%.

More bilingual patients had normal cognition (40.5% vs 19.6%; P < .0001), and more monolingual participants had cognitive impairment (vascular dementia or vascular mild cognitive impairment) (77.7% vs 49.0%; P = .0009).

Aphasia Rates

There was no difference between the two groups in aphasia (11.8% for monolinguals vs 10.5% for bilinguals; P = .354).

This, said Dr Alladi, is in line with research suggesting that the mechanism underlying the protective effect of bilingualism is not better linguistic ability but executive function gained through a lifelong practice of switching languages.

"When one is bilingual, executive function is thought to improve, but that seems to come at a cost to linguistic processing; monolinguals are actually outperforming bilinguals on that," said Dr Alladi.

When comparing patients with normal and impaired cognition, researchers found that in addition to monolingualism, older age, lower educational and occupational status, and vascular risk factors were significantly (P < .003) associated with post-stroke cognitive impairment.

In a series of logistic regression analyses that examined demographic variables (age, bilingualism, sex, education, occupation), stroke-related variables (left-sided infarcts, previous stroke, infarct location, time between stroke and assessment), and stroke risk factors (hypertension, alcoholism, smoking, cardiac disease, diabetes, family history of dementia), the authors showed variance of 31%, 24%, and 28%, respectively.

In a final regression model, the study showed that bilingualism and age (both P < .001) were significant independent predictors of cognitive impairment, with an odds ratio of 3.007 for bilingualism and 1.026 for age.

Since the groups had similar vascular risk factors and were about the same age, the results suggest that the differences are not due to a healthier lifestyle.

Cognition following a stroke is important to study because more than half of stroke patients have some sort of cognitive problem, said Dr Alladi.

Several studies have looked at language and dementia not in the context of stroke, noted Dr Alladi. One study showed that people who are bilingual have an onset of dementia 4.5 years later than people able to speak only one language.

There's evidence that Austria, where many citizens are trilingual, has a relatively low prevalence of dementia, she said.

Activated Networks

To comment on this study, Medscape Medical News invited Jose Biller, MD, professor and chair, Department of Neurology, Loyola Medicine, Maywood, Illinois, who himself is bilingual, having spoken Spanish from childhood and learned English as an adolescent. Dr Biller called the study "very intriguing."

What was particularly interesting, he said, was that it found no group differences in aphasia.

Dr Biller cited a study by researchers at University College London that compared language outcomes in mono- and bilingual stroke patients (Brain. 2015;138(Pt 4):1070-1083). The study sought to establish how applicable post-stroke prognostic models, trained with monolingual patient data, are to bilingual stroke patients in the United Kingdom.

The study pointed out that research into the recovery of language function is almost exclusively focused on monolingual stroke patients, but bilingualism is the norm in many parts of the world.

"I'm intrigued by this issue of language outcome in mono- and bilingualism because if bilingual language recruits different networks in the brain, obviously the prognostic models that are developed usually for monolinguals may not be applicable for bilingual stroke patients," commented Dr Biller.

The bilingual patients in the Brain study tended to have poorer language skills than expected, based on trends learned from monolingual data alone, and this was significant (P < 0.05, corrected for multiple comparisons) in 13 of 22 language tasks, according to the study authors.

Both patient groups appeared to be sensitive to damage in the same sets of regions, although the bilingual participants were more sensitive than the monolinguals.

The new study by Dr Alladi and her colleagues is in line with research showing that "bilingualism offers some advantages in executive function," likely through plastic changes in the brain that "may activate some neural networks that are not activated or involved in monolingualism," commented Dr Biller.

He noted, as did Dr Alladi, that evidence indicates that the ability to speak multiple languages may delay the age of dementia onset by several years.

And some early research is showing that acquiring a second language even in adulthood may still afford some cognitive protection, said Dr Biller.

He also pointed out that the region of India where the study was carried out has a "very heterogeneous" population, and where languages such as Telugu, Urdu, Hindi, and English are commonly spoken. "So it's hard to be certain how much you can extrapolate from this observation to the rest of the world."

Further studies are needed, stressed Dr. Biller.

This study was funded by the Indian Council of Medical Research. The authors have disclosed no relevant financial relationships.

Stroke. Published online November 19, 2015. Abstract

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